


The Little Mer-Tsum

by Dodo



Series: Tsum Tsumsery [15]
Category: Marvel Cinematic Universe
Genre: Anal Sex, Beta/Beta, Come Inflation, Crack, Lingerie, M/M, Mermen, Pregnancy, Rimming, Smut, Strip Tease, Tsum Tsums, steve's huge dick
Language: English
Status: Completed
Published: 2020-05-26
Updated: 2020-05-26
Packaged: 2021-03-02 19:02:13
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,361
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24381751
Author URL: https://archiveofourown.org/users/Dodo/pseuds/Dodo
Summary: He wanted to be where the people were, but after rescuing the shiny flying man, Steve finds he doesn’t mind staying with the awkward land tsum, for the rest of his days.
Relationships: Steve Rogers/Tony Stark
Series: Tsum Tsumsery [15]
Series URL: https://archiveofourown.org/series/1364983
Comments: 13
Kudos: 56
Collections: POTS (18+) Smol Steve Appreciation Bingo





	The Little Mer-Tsum

**Author's Note:**

> Mermaid/man fill for the pots server
> 
> but also filling my need for more tsum tsum porn.

He’d been told time and time again not to follow the ships and yet here Steve was following in the wake of a ship, it was easier he thought to swim in front of the boat but, it was also easier to be spotted and he did get tired quickly as well. Rumors that the land tsum would hunt a mer-tsum down. Harpoon them and do terrible things, anything from leaving them trapped in tiny tanks to carving them up into very small pieces for unspecified reasons.

In Steve’s case a tank and being fed for the rest of his life sounded ideal. He was so very small for a southern right whale mer-tsum. He was still about the same size he was when he was prematurely weaned from his mother. He didn’t really have a pod, bucky had gone off long ago to do some fighting for the mer-war. He never returned, Steve really didn’t have anything else so when Bucky failed to return the first year, then the second, and finally the third Steve decided to go look for him.

A grand Idea at first, right now he was hopelessly lost and following ships because he found them interesting with their sputtering and juddering. Of course the strangely round pill shaped land tsums were fun to look at! They looked like sea cucumbers. They were so clumsy sometimes at night when the ships slowed down he’d climb up to peek through the railings and watch them wiggle and waddle. They reminded Steve of penguins trying to be elegant and failing at locomotion.

They spoke in a strange dialect and had many crates on their deck. Of course he recognized the guns, similar make and branding to the ones that had been used against the mer-tsums, reminding Steve that he should really be looking for Bucky. Shoulders slumping he didn’t even know where to go at this moment, even if Bucky was alive how would he find him?

He slid back into the water letting the boat move away as he stared listlessly at the starry sky. There was a shooting star, zipping past Steve. The water churned around him and he dipped below the surface and followed the bright light that he thought was a star. It landed on the boat, Steve kicked his tail as he neared the vessel again, there was gun fire, shouts, and fire. The Star was spitting fire, which made sense to Steve as it was a “star”. He cheered as the bright little star blew up the caches of weapons, and fought against the many land tsums.

Steve watched the ship lurch in the water and he swam farther away from it. He’d seen how these vessels went down. He wasn’t a confident swimmer like Bucky, so he gave the ship some room to sink. The Star however was propelled into the water with another mighty explosion. Steve dove for it, he knew star’s didn’t care for water. Spotting the red and gold shiny star under the water he swam to it banging his nubs on it trying to wake it up.

No use, he pushed the heavy body of the star up to the surface and looked around. There were burning bits of the ship and other land tsums complaining. He looked up at the sky getting his bearings and swimming for the atoll he’d passed by a day earlier. Using some rope he tried the star to him, and swam. It was very heavy and while Steve wasn’t certain where the star’s face was, he went on how the nubs were oriented. It was still breathing, that was good. Steve took another deep breath as he dove under the water, the Star was behind him on the surface still as he swam.

It was easier to swim under the water but less efficient since he was dragging the star, but if he stopped moving the star would sink and die. Steve wouldn’t let that happen, he rolled the Star up on the beach as far as he could that didn’t beach himself. Wiggling back into the ocean he decided to get some food and the return to see if the star could fly again, maybe even offer some of the food to the star.   
-  
Tony groaned and wiggled out of his armor, he was sore but alive. He looked around the island he was on, very small and the surrounding water seemed calm. He poked Jarvis a bit, still soggy. His under suit was also still moist, and parts of it were shredded, but it was mostly intact. He dragged his armor towards the tree line and flopped down in the shade. He had not been expecting such retaliation on the ship. If only he’d sunk it and flew home.

Though then those hydra water Tsums would probably salvage his tech off the ocean floor and he’d have to hunt them and destroy it yet again.  
“Tsum,”  
He grumbled to the armor as Jarvis rebooted. He needed to make the suit waterproof. The under suit was chafing his backside. With it still damp it was very hard to remove so Tony decided to head down to the water to get it off, and drape it on one of the flat rocks that dotted the beach.

He shimmied in the shallows and slowly pulled off his under suit while swishing around in the shallow waters. So he’d been wearing his red lacy lingerie because there was no real reason. That made him feel pretty and they worked really well with the under suit, luckily he was alone. Or so he thought as he wiggled his hips and turned his face to the sea to see the wide blue eyes of another tsum.  
“Tsum!”

Tony jumped back, the other tsum edged closer but seemed to be having trouble in the shallows. Tony looked down to see a blue grey fluke with white flecks. A Mer-Tsum! Vague memories of a tsum dragging him in the ocean, this one had rescued him.  
“Tsum?”

‘Star?’ Tony looked back at his armor and it was shining in the sun, the other Tsum looked at it then wiggled closer. Tony hopped up and then tripped over on his back in the sand as the mer-tsum checked over his red intimates. One nub under the hip string shocked Tony into motion and he rolled back to his feet.

“Hey!”  
“Star? I brought you food.”  
The mer-tsum offered a crab hesitantly. Tony shrugged and carefully accepted the crab and trotted off to his armor to cook it. Trying to keep some distance away from the cute mer-tsum. Who was now inspecting his under suit, with great curiosity.  
-  
The star had shed it's outside and an inner layer. Steve was starting to suspect it was just a land tsum and not an actual celestial being. That would have bothered Steve at first but, now well the land tsum was kinda cute, and the red smooth things. They felt nice against his nubs, he was just trying to see if this land tsum had a pearl fish. Had to make sure after all.

He could smell the crab cooking, father up the beach. The tsum had mastered fire, and was staying away from the shore line. Steve slid back into the waves pushing his body back into the surf. Kicking his tail out as he dove under the waves and swam out to where the ship wreckage was. Maybe he could find something for the land tsum? Something that would make them less scared of him.

If that was even possibly Steve was pretty underwhelming. His whale tale was skinny, his tsum tum was concave, he looked sickly. He pushed forward, kicking the water with his frustration.He could see some of the floating bits of debri from the explosion, he gathered up some of the flotsam, using the rope bits he found along the way and picked through the salvage. He found a dingy with a tool box in it. That was the best find, he dumped the stuff he’d been dragging along.

Pulling the dingy back was harder than swimming with the star. The boat had considerable more drag, and he felt like no amount of his kicks were propelling him anywhere. He frowned had he been weaker than he originally thought?

No, he’d just never pulled a boat that could fit several land tsums in it. Maybe with the boat the land tsum would look at him? Steve breached and huffed, he needed some air. Thinking about the land tsum dancing in the water and removing that black skin. How the sea cucumber like tsum had managed to be graceful in the water. The way the star had moved their hips, the red material shifted, Steve frowned and he was cold all of a sudden.

Ah! He should probably stop thinking about the land tsum curvaceous back side, he was now making even more drag. He cursed at his penis under the water out of everything he had, skinny, sickly, small, and a monster cock. Bucky had always made light of it, saying Steve was a “grower” as if. Steve felt his body poured all of its resources into his penis and skimped on everything else.

He pushed down the memory of the Star’s strip dance, and tugged the boat towards the atoll. Hoping the star was still there. He managed to get the boat up on the land as far from the tidal zone as he could. However Steve just collapsed in the shade of the boat, the waves and ocean looking far away at the moment and he just wanted to take a nap.  
-  
Tony came down the beach to dump the crab bits off and thank the mer-tsum for it. The meat had been sweet and filling. He paused upon the sight of the row boat and then dropping the crab shell raced toward it, excited this could be a chance to get back home! He found a tool box inside the boat's hull along with more wood, rope, and a tattered tarp.

Tony pulled back and checked around the bow, and sure enough he found the mer-tsum. The merman must have gone out of his way to bring back some of the salvage, and to push it up onto the beach like so. Tony patted the soft golden locks, the mer did not stir. His skin on his tail looked cracked and dry, his pale skin was pinking under the dying of the sun.  
“Tsum!”

Tony knew what he had to do and tucked his head under the mer-tsum’s belly and shouldered the limp body and he made his way back to the ocean. He placed the little mer-tsum in a nearby tide pool, propping the other tsum’s body against the soft algae covered rocks as he fetched some of the seaweed he knew could help with sunburns. Having treated his own burns with it. Thankfully Jarvis has helped him the first time.

Tony chewed on the seaweed, spitting it out on the mer-stum’s back where the burn was the worst and spreading it around till it made a nice thick green paste. He placed some of it around the dorsal fin as well. Dipping himself into the pool to rub the rest of the stuff on the tail, Tony encountered the biggest dick he’d ever seen.   
“Tsum…”

His eyes shining as he watched it grow in size his own movements faltered in the rubbing.  
“Tsuuu,”  
The mer-tsum was waking up, herring the soft voice of the other grumble. The tail kicked some water at Tony and he pulled away blinking the saltwater out of his eyes.  
“AH!”  
The mer-tsum tried to cover himself but flinched, the burned skin didn’t stretch. He instead hid his face with his nubs from Tony.  
“Ah, hey thanks for the boat, and all…”  
Tony patted the mer-tsum’s hip eyes drifting back to the dick, he licked his lips. 

“Let me take care of that for you.”  
“Really?”  
The soft hesitant voice of the mer-tsum broke Tony’s staring match with the dick.  
“Of course! You risked your life to get me some stuff, and you saved my life.”  
“I thought you were a star.”  
The mer-tsum sounded defeated.  
“Trust me, I am! Tony’s the name.”  
“I’m Steve.”

“Okay Steve, I’m going to take care of this and then it's my turn to get some food.”  
It was probably going to be coconuts and those little tubers that Tony had found. He could try fishing though he was certain that he wouldn’t catch anything without Jarvis’ help and his suit was pretty much immobile. 

He leaned down and touched the base of the dick Steve squirmed under his nub. Tail quivering.  
“Steve, can you relax?”  
“Do you want to touch me?”  
Tony blinked at the question.  
“Of course, you’re pretty cute. My savior.”  
“I think you’re cute too.”  
Steve admitted, face turning red behind his nubs.  
“Oh you do? I bet it's my butt.”  
“Yes, you look really nice in those red things.”  
“How about you roll on your back, and I uhh let me get into something more comfortable.”  
-  
Steve had to peek from his nubs and he was glad he did, to see Tony turning around wiggling his hips as he removed the red shiny fabric bits. Steve could now confirm that there was no pearl fish in Tony's butt, and the way Tony kept looking at his dick probably meant something real good. This would be Steve’s first time, he rolled on to his back his burned skin was tingly and numb from the seaweed paste Tony had applied.

Tony winked at Steve, who felt even more flush if that was possible and then the top bit of the red fabric was shed, and wrapped around his cock.  
“Oh!”  
Steve jerked the fabric was very smooth and there was a bit of a tickle to it.  
“Lace and silk, feels great.”  
“Yeah,”  
Steve managed to respond but nearly breathless and not very articulate. Tony climbed precariously on top facing away. Giving Steve’s dick one a long languorous lick.  
“Tony!”

Steve’s by thrusted up and Tony managed to stay on top of Steve but it was a near thing. He gave Steve a wink and took the head in his mouth and sucked it. Steve’s vision whitened and he moaned bucking against Tony’s warm wet mouth it was nothing like swimming in the ocean. Bucky had lied! He was getting his bearings back when he noticed Tony was trying to put his penis inside his butt.  
“Face me? Tony?”  
“Ah, don’t you want to see it disappear in my ass?”

Steve paused yes he really did, but not for his first time. He chewed on his lip and raised his gaze to meet Tony’s.  
“Yes, but we can do that later, I want this to be special!”  
“”Later?”  
Tony grinned, patting Steve’s hip as he wiggled around to face the other.  
“I like that idea, Later sex!”

Tony wiggled his butt up against Steve’s cock, rubbing the crack against his head like a tease. Tony did a wiggle and lifted a leg and Steve’s dick slid in with ease. It was tight and warm, Steve bucked up and Tony wiggled down. Tony’s face was pink and his beans hung around his face, Steve curled up to kiss that face thinking the beard would be soft. It wasn’t as soft as the algae, but it did have a nice texture.

Steve reached for Tony with his nubs, the tight feeling and the heat that pooled in his belly was nearly overwhelming. Tony reached out and grabbed Steve with his nubs.  
“Steve, mmm. See that? That's you.”  
Tony pointed to a section of his round body that would bulge out when Steve thrusted into Tony. He touched the spot marveling at the feel of his own dick thumping against his nub.  
“Does it hurt?”  
He was worried about hurting Tony. Tony barked out a laugh.  
“No, it feels really good. I can hardly wait for later sex. Where you have me under you on the surf and you fuck the life back into me.”

Steve sputtered frowning at Tony’s smug face and he pushed back into Tony with more effort. If he was going to fuck life back into him, he’d better fuck the life out first. Tony’s mouth dropped into an O-shape and Steve kept at the faster pace thinking it was just like the races. This time Steve didn’t have to worry about losing though. He pumped into Tony watching the other bounce on his cock. Tony’s own dick bounced between them slapping against the skin.

Steve pressed on watching Tony slide up and down on his length. Riding him, Tony started to get a bit more jerky, his movements not as smooth and then he came all over Steve’s chest.   
“Fill me up, stud.”  
Tony spoke in a slurred manner, his body drooped and the only thing keeping him up was Steve’s dick.  
“I could do this all day!”

It was a boast, but the idea of having sex with tony all day urged Steve on as he thrust into Tony’s firm tight buttocks. Feeling his dick move within Tony as he pressed in deep. Thinking about how much easier it would be to do this with Tony under him. He tugged On Tony’s nubs holding the other down as he came in thick warm ropes. His body had always been an over producer of cum, he laid there bliss-ed out as his cock rippled with another cascade of cum. Watching Tony’s firm tummy grow a bit with each round.

Tony was awake moaning and his hole twitched around Steve’s dick. Tony leaned back and Steve came again, Tony’s face was pink and he smiled at Steve.  
“Wow, you really did fill me up.”

“I’m not done, the tide is going out and now you can be under me.”  
“Heh, sounds good. Any time Steve, I’m down for a hot dicking from you, any time.”  
“Now, I want to make you round.”  
“I, that's hot. Ugh how much do you? Can you?”  
Steve nodded, and Tony smiled.  
“Make me round Steve.”  
-  
Tony was laying on the beach with an improvised butt-pug in his ass basking in the sunlight. Steve had fucked him thrice before needed to get some food for them both, he was ample in the middle. Made a promise not to remove the plug, but had managed to fix the suit somewhat while waiting. Jarvis was currently trying to reach out to shield, see if they could be located and rescued. Though Tony wasn’t sure if he wanted to leave.

He was very much in love with Steve, the smaller mer-tsum had been quite the lover. The last coupling Tony had got to be on top and took his time teasing the other. Describing his butt as cock hungry had done it for Steve who was surprisingly weak to dirty talk. Tony wasn’t even sure if land-tsums and mer-tsums could have babies. He patted his belly he kinda wished they could? 

He would investigate that idea later, he could see Steve. He waved his nub as he waddled closer to the surf. He was wearing his silk panties because they did things to Steve, and he wasn’t above tempting fate. Steve had food of course fish, and Tony showed him how to make the fire. Steve was a quick study with learning.

Tony munched on the fish happily, letting Steve what he’d done. Wiggling his bum as he cleaned up the food remains and then he was being dragged back by his hips and his lacy things being pulled off. Steve was licking his ass, nub tugging at the plug. Tony pushed back, into Steve’s face letting that tongue lick up his musk and Steve’s cum.

“Mm Tony you taste great.”  
The plug was pulled free and tony felt his muscles flutter with the loss of the heavy plug. Steve slowly sheathed himself into Tony. He sighed relaxed as Steve’s dick pressed up against his pleasure spot.  
“This is life!.”  
“Tony, I don’t want this to end.”  
Steve admitted into his ear. Tony cracked his eye and looked up at Steve.  
“Me too, come with me?

“Where?”  
“Anywhere, with me.”  
“Yes!”  
Tony would figure out a way to make any of his homes mer-tsum friendly, the Malibu one already had a bunch of water features he could probably connect them so Steve could get around, and there was the ocean right there too! All thought of re-engineering his house stopped when Steve pressed down.  
“Ah!~”

“I’mma making you round!”  
“Oh yes Steve you are! I can’t wait to make you round.”  
Steve faltered in his thrust, his voice was small.  
”Y-you’d do that?”  
“Of course!”  
“I thought you liked my cock?”  
Tony turned as best he could to see Steve’s open and vulnerable face.  
“I like you Steve, and everything about you!”

Steve picked up his pace,  
“I want to be round and full of you Tony.”  
Tony groaned, Steve was saying such dirty things with such wholesome adoration. It went straight to his cock. He squirted out all over the beach, groaning because he could have cum into Steve but also as his fourth orgasm rocked into him.  
-  
Steve was bouncing himself on Tony’s dick it was smaller but Steve thought it was the perfect size. Tony was still in a fugue, so Steve had plugged him up and taken his turn on Tony’s still hard cock. He patted his concave tummy thinking about it being as filled and round as Tony’s made him very happy.

It wasn’t as easy this way with his tail, but it worked for now. Tony stirred under him, the nubs were moving in a slow movement like he was trying to walk. Steve patted Tony’s face, petting the beard it was nice, when they kissed it made a tingly feeling along Steve’s cheeks.  
“Ah Steve, I uh.”  
“Make me round!”  
Steve bounced enthusiastically on Tony.  
“I don’t cum as much as you, but I will try my best!”  
Tony hastily tacked on the end part, when he saw Steve’s grin fall.

Steve managed to wringe out two more orgams from Tony, which only made Tony distantly think they were a perfect match coming so much in just a day and a half. Steve also carefully placed Tony’s red panties back on, and brought over his undersuit. The mer-tsum had noticed that Tony was turning a different color and had worried about the tan. The under suit really didn’t fit with Tony’s inflated tummy so he wore it but with the zipper unzipped.

Jarvis had managed to reach Shield and there were sending a quinjet to pick him up. So everything was being stored in the boat, as they waited. Steve brought another crab or two and they ate in silence. Steve seemingly didn’t want to risk having more sex and having strangers seeing him and Tony conjoined.  
“It's private, I don’t want to share.”  
“Ah I understand.”  
“They can see you round.”  
“st-EVE”

Tony sputtered around a bite of the crab, Steve smiled back, face all flushed. He looked a bit ethereal with the oceans waves lapping at his sides.  
-  
Tony kicked his legs as he sat on the cot in the med-bay, a lot had happened after being rescued by Shield. First off Steve had recognized the man that had come to save them, Bucky apparently had once been a mer-tsum. He was no longer and had been searching for Steve ever since he’d come back to his own mind.

Steve apparently had been swimming in circles ‘looking for Bucky’, no tsum had dared mention that to Steve though. The second was Steve was now being pushed around by his friend in a tank on a dolly. Actually the second was Steve was preggy, he’d started showing signs of it within the week of acclimation. The mer-tsum had loudly declared that ‘Tony had made him round!’. Which turned out with clarification from Bucky had been one of Steve’s dreams in life to be a round fat mer-tsum.

Third, well it wasn’t too big in the grad scheme of things but Tony thought it had to count for something. They were both betas, which made the next reason more amazing on the cross species fertility argument. It had been traditional though only an omega and alpha of either species could cross breed. Not that there were any examples, it was just assumed that pairing had a better chance. Tony was all about disproving traditional values.

Fourthly, the reason Tony was even here in the med bay butt naked with a paper sheet on the cot propped up so he could look over his very round belly. He was also pregnant, and was here for a check up. Setting a precedent for land tsum and mer tsum populations it seemed. The merfolk had nominated Steve as their ambassador. Strangely enough, probably had to do with Hydra being a constant looming threat. They had a power to turn mer-tsums into land tsums. 

Steve was wheeled in, he was looking around eagerly, eyes shining when they landed upon Tony’s form. Tony stopped kicking his legs and waved at Steve, Bucky parked him close by so he could see the ultrasound images. Bruce toddled in with his charts. Still muttering about the odds of cross species reproduction.  
“Only you Tony could have done this,”

Holding out the print off of four tiny heartbeats.  
“I’m really big for just four.”  
“Two of them have tails.”  
“Ah, I guess I should make the indoor swimming areas bigger.”  
Steve nodded from his tank, having been going over the housing improvements with Tony. Eager to raise his pups with Tony, with Bucky helping they would be fine. He dipped under the water quietly waiting for his turn. 

Everything had worked out for him, he’d found Bucky, he was finally round, and he had the prettiest land tsum as a mate. What more could the littlest mer-tsum want?


End file.
